Field of the Invention
The present disclosure relates to an ink and a method for producing the same, and an ink stored container, a printing method, and a printing apparatus.
Description of the Related Art
Compared with other printing methods, inkjet printing methods have advantages that inkjet printing methods have simple processes, can be easily accommodated to full-color operations, and can provide high-resolution images even when used on apparatuses having simple configurations. These advantages have made the inkjet printing methods popular and are spreading the inkjet printing methods to personal and office uses and commercial printing and industrial printing fields.
In the inkjet printing methods, water-based ink compositions using water-soluble dyes as coloring materials are mainly used. However, pigment inks using water-insoluble pigments are being developed to replace the water-soluble dyes, because the water-soluble dyes have disadvantages of being poor in water resistance and light resistance.
In inkjet printing in offices, plain paper is mainly used as print media, and a high image density is demanded on plain paper. Generally, when a pigment ink is printed on plain paper, the pigment does not stop at the surface of the paper but permeates the internal portion of the paper. This makes the pigment density on the surface of the paper low and makes the image density low. Increasing the pigment concentration in the ink leads to a higher image density, but also to a higher ink viscosity and a poorer discharging stability.
There is also a problem that immediately after pigment ink droplets land on plain paper, water in the ink swells the surface of the paper to generate a large difference in the stretching rate between the top and bottom surfaces, to make the paper curl. This phenomenon diminishes as the paper dries and has not been problematic in low-speed printing. However, advancement in the printing speed entails the print medium to be conveyed before the curling of the print medium after printing diminishes. This may cause a paper jam. In order to prevent this problem, there are proposed a method of adding a permeating agent in order for water to quickly permeate paper, and a method of adding a hydrophilic organic solvent in a water-based ink. However, this makes the ink hydrophobic, to make it harder to secure ink storage stability. This makes also the pigment highly permeable into the print medium, leading to a further degradation of image density.
Unlike water-based dye inks prepared by dissolving dyes in water, water-based pigment inks used in the inkjet printing methods and as writing materials need water-insoluble pigments to be dispersed in water stably for a long term. Therefore, in order to solve the problems described above, various pigment dispersants are being developed.
As a technique for improving ink storage stability, there is proposed a polymer containing, for example, a repeating unit containing an aromatic ring and a repeating unit containing an ionic group (see, e.g., Japanese Unexamined Patent Application Publication No. 2009-299005).
There is also proposed a polymer formed of a monomer containing an acidic group of carboxylic acid or sulfonic acid and a salt derivative of the acidic group and a monomer containing a partial structure derived from naphthalene (see, e.g., Japanese Unexamined Patent Application Publication No. 2007-153976).
There are also proposed techniques of using a polymer containing a specific partial structure containing naphthalene as a pigment dispersant (see, e.g., Japanese Unexamined Patent Application Publication No. 2015-117354 and U.S. Patent Application Publication No. 2016/0017075).